History says neutrinos are where to look for new physics, so current research obliges.

Some physicists are surprised that two relatively recent discoveries in their field have captured so much widespread attention: cosmic inflation, the ballooning expansion of the baby universe, and the Higgs boson, which endows other particles with mass. These are heady and interesting concepts, but, in one sense, what's new about them is downright boring.

These discoveries suggest that so far, our prevailing theories governing large and small—the Big Bang and the Standard Model of subatomic particles and forces—are accurate, good to go. But both cosmic inflation and the Higgs boson fall short of unifying these phenomena and explaining the deepest cosmic questions. “The Standard Model, as it stands, has no good explanation for why the Universe has anything in it at all,” says Mark Messier, physics professor at Indiana University and spokesman for an under-construction particle detector.

To go beyond the models we already have, beyond the confines of the Standard Model, we need some results that we don’t foresee. And when it comes to unexpected results, we expect them from one entity: neutrinos. These particles are abundant, ineffably light, and very weird, but they consistently deliver.

Ethereal as they are, neutrinos could make hefty changes to our understanding of the universe if physicists could answer four main questions: How does regular matter affect neutrinos? What causes neutrinos to have mass? Do antineutrinos live different lives from normal neutrinos? And even odder, are these ghostly particles their own antiparticles?

The Standard Model, which physicists have populated since the 1950s with quarks, leptons, and force-carrying particles, does not hold the answers. But major neutrino experiments in the US, Japan, and Europe are collecting data while undergoing expansion and construction, and they are gearing up to address these problems. These initiatives could not only unravel the mysteries of the ghostly particles, but the research might lead into larger questions about the nature of all things.

What’s the matter with neutrinos?

Neutrinos are the second most abundant particles in the Universe (after photons), but they carry no charge and are puny. Neutrinos are at least a million times lighter than an electron, though no experiment has been able to definitively measure their mass. They also barely interact with any matter. They are generated in distant supernovae and travel unhindered through the debris. Neutrinos zip through planets in a single bound without leaving a trace. Billions and billions of them are streaming from the Sun as you read this, blowing through your screen—and through you—without a care. They travel extremely close to the speed of light; so close, in fact, that a tiny error in an experiment designed to measure them was enough to make it appear that they were going faster than that in 2011.

But perhaps the neutrino's strangest property is that they don’t necessarily finish their travels with the same identity that they started it with.

In 1998, the 11,000 phototubes submerged in Japan’s Super-Kamiokande underground detector verified that neutrinos coming down through the atmosphere and up through the Earth had different ratios among their identities. Somewhere along their journey from the Sun, they changed type among their three flavors. This oscillation indicated they indeed had mass. If they didn’t, there wouldn’t be anything to switch between.

Finding out anything about these particles has been difficult because neutrinos are so notoriously hard to detect and to obtain. But there are now a few ways to do this. Experimenters can nab some from the Sun, like Super-K and many others do. Or they can situate detectors near nuclear reactors, which produce electron antineutrinos. The Daya Bay Reactor Neutrino Experiment in southern China listens to these particles. Finally, physicists can fire up particle accelerators and smash protons into bits of graphite, creating a neutrino spray in the process. The latter is the goal of forthcoming experiments like the Long Baseline Neutrino Experiment, under construction at Fermilab, and the Japanese Tokai to Kamioka experiment, which runs from the seaside town of Tokai to the Super-K detector. Manmade neutrinos are easier to lasso than their incidental brethren, but because of their quantum nature, detecting them is a probabilistic challenge.

“Every time we were able to measure a property of neutrinos, we were surprised by it,” says Patrick Huber, a neutrino theorist and associate physics professor at Virginia Tech.

Neutrino flavors—electron, muon, and tau—aren’t discrete individual particles, but combinations of the neutrinos’ different masses. These masses are related to the neutrinos’ energies, as Einstein taught us in E=mc². Although a neutrino can be produced with a specific energy, and thus specific flavor (the Sun makes a multitude of electron neutrinos, for example), the quantum state of these neutrinos is a mixture of all three that twists in time. “They are just inherently quantum mechanical. If I gave you an electron, and I ask you 10 minutes from now, ‘do you have an electron in your hand?’ the answer would be yes,” Messier says. “Neutrinos just break that.”

What are some of the things that they break? Though neutrinos have vanishingly small masses, regular matter can rub off on them, like a sourpuss spoiling the mood at a dinner party. Robert Wilson, physics professor at Colorado State University and spokesman for the Long-Baseline Neutrino Experiment (LBNE), likens neutrinos to light passing through a filter. Some wavelengths are affected while others aren’t. Similarly, certain neutrino flavors seem to be affected by regular matter as they zip by.

Last month, Japanese experimenters demonstrated this oscillation effect by finding that neutrinos shine more brightly at night. As electron neutrinos stream from the Sun toward Earth, they oscillate to muon and tau neutrinos. But as they pass through the dense matter of our planet, some of them switch back. This suggests some quantum-mechanical transformation is taking place as the neutrinos interact with matter in the Earth, specifically its electrons. The electron neutrinos can exchange a W boson, the carrier of the weak force, during this interaction, according to Messier.

“They are sort of kissing the electrons and moving on. This is a weak force interaction,” he says. “The W boson changes the phase of its wave without changing its momentum. That’s the possibility that introduces this matter effect.”

LBNE will take a hard look at these matter-related effects, which cause droplets of electron neutrinos to appear amid a shower of muon neutrinos. Fermilab’s accelerators will stream neutrinos 800 miles toward a liquid argon detector buried beneath South Dakota bedrock. The detector distances are in a sweet spot that should allow physicists to not only study matter effects, but to also search for clues as to why the Universe contains any matter for them to interact with in the first place.

That’s because this wee effect has important implications for the asymmetry between matter and antimatter, says Wilson. “It’s still the neutrino; it hasn’t changed in one sense. But the probability of what you will see when you make the measurement has changed, and it depends on how much mass it has gone through.”

At Fermilab, they know detectors only have a small chance of seeing neutrinos—so they build lots of detectors.

John Timmer

And what of their own masses? The Standard Model can’t explain that either. Based on the variable buzz rate of neutrino masses, physicists have been able to tell that they’re different, although no one is sure how they stack up. We don't yet know which neutrino is heaviest, which is lightest. An upcoming detector called the NuMI Off-axis ve Appearance experiment, or NOvA, will help determine neutrino mass hierarchy. NuMI is a neutrino beam at Fermilab; NOvA’s 14,000-ton detector will look for a disparity between departing muon neutrinos and arriving electron neutrinos (ve).

Even if this experiment succeeds in generating new mass data, physicists won’t be able to say exactly how that mass arises. Because neutrinos are so much lighter than any other particle, the Higgs mechanism is unlikely to endow them with mass the way it does other particles, Messier says.

“There must be some mechanism that suppresses their masses,” Messier says. “And what are the masses? What pattern do they follow? What’s the pattern of that mixing? It’s launched a whole experimental program to pull apart that crack in the Standard Model.”

LBNE, NOvA, and other upcoming experiments will attempt to pull those cracks until the Standard Model shatters completely. From the debris, these research initiatives hope to build a new theory of physics.

"relatively recent discoveries in their field have captured so much widespread attention: cosmic inflation, the ballooning expansion of the baby universe"

Recent? How old are you?!

We knew the universe was expanding when Hubble discovered most galaxies are red shifted.

The theory of inflation was postulated in 1980 by Alan Guth. It was not until March 17th of this year (2014) that we measured gravitational waves in the CMB, giving us serious experimental evidence for inflation. I'm going to call a month and a half recent.

You're confusion is because you conflated expansion with inflation. Expansion is what's happening, inflation is the theorized mechanism.

Any article about big neutrino science ought to mention SNOLAB, under 2km of the Canadian Shield near Sudbury. They're just starting up their new SNO+ detector, replacing the heavy water from the old detector with "LAB" scintillator.

Physicists too, I have a feeling, are sometimes hoping they will find something that breaks old models, to make a name for themselves and secure more funding perhaps.

While fame and fortune may play a role, I think there is a more fundamental aspect: there are certain things that he Standard Model just does not explain. Among them, why neutrinos have mass, why the universe has more matter than antimatter, what dark matter and dark energy are, and how gravity works.

Neutrinos are certainly a good candidate for discovering something new. A solar correlation to radioactive decay-rate variations in Radium-226 was supposedly seen back in '08. (http://arxiv.org/abs/0808.3283) I believe a similar effect was later noted in Plutonium by some other researchers. If this represented an effect on Alpha decay, it might suggest some new solar neutrino physics (possibly involving a Strong interaction or some unknown force).

The sensationalist reporting over the Higgs is mostly due to the popularity of calling it the "God Particle" from a book by the same name. It's not so much the discoveries themselves, the physics why this is significant goes over most people's heads and that's understandable. Those stories were meant to capture headlines rather than relate what the discovery meant to the average person. Arguably that would be practically nothing by itself.

Neutrino experiments aren't new either. We've been looking for neutrino oscillations since the late 80s, and neutrino detection was the primary focus in the lab I worked in as an undergrad in the early 90s. The main focus shifted from giant expensive projects like the SSC and into smaller, cheaper, and possibly more efficient experiments on detecting neutrinos and gravity waves like the gravity wave observatory in S. Louisiana. Backlash from the expensive hole in the ground that was supposed to be the SSC required physics in the US to look for relatively cheap ways to do the same work (millions versus billions). For example: using inexpensive x86 embedded systems for control and telemetry rather than MIL spec hardware which cost 10x as much as was traditionally used in government grant work.

The Higgs is definitely a significant discovery as is discovering neutrinos oscillate between states. I would posit that 'interest' mostly lays in the current political climate and whoever can wheedle the most support from colleagues that control the purse strings. Standard Model is in, alternatives are currently out. Supporting experimentation is therefore 'in', while looking directly for alternative theory corroboration is 'out'. That could very well change in the next decade just like it did for relativity at the beginning of the 20th century.

My personal take on the the Standard Model is colored by my adviser at the time. The Standard Model is missing something somewhere. Where is still being looked for, but it's not the perfect model as some physicists like to make out. You'd have to debate that with her, however, as I've not delved into the concepts on a nit picky level since my university days.

Physicists too, I have a feeling, are sometimes hoping they will find something that breaks old models, to make a name for themselves and secure more funding perhaps.

While fame and fortune may play a role, I think there is a more fundamental aspect: there are certain things that he Standard Model just does not explain. Among them, why neutrinos have mass, why the universe has more matter than antimatter, what dark matter and dark energy are, and how gravity works.

Considering all (provable or counter-provable) possibilities is always the fundamental idea behind science, and I daresay physics the epitaph of it. Wave-particle duality was established only by "breaking" old models set by Newton, Maxwell and Hertz respectively in their time. Sometimes an oddity such as Technicolor pops up, but nonetheless challenging is an important part of the procedure.

While I think this is interesting research, I am somewhat upset over the attitude which may have been expressed in the opening. That is, something must upend or supersede existing models to be interesting or worthy. How interested is the public in learning the things that we already know, versus the things we are trying to find out?Physicists too, I have a feeling, are sometimes hoping they will find something that breaks old models, to make a name for themselves and secure more funding perhaps.

There are still important unanswered problems, and things to explore. I just think perhaps these attitudes are a bit unhealthy.

You can do good and useful science proving existing theories, sure. But face it, current physics is not so great. We have no antigravity, we have no FTL travel. I'm looking for big shake-ups too!

to respond to those arguing that physicists may have ulterior motives for wanting new and theory-clasting breakthroughs, i.e.. fame, fortune, etc; i posit that while almost no human with an ego would deny the pleasures in having one's good works recognized, i would argue that the vast majority of physicists are in the game for the sheer love of understanding and discovery. and while the standard model is not broken or in need of trashing and starting over, there are a number of aspects that make it tantalizingly ripe for a re-think, or deeper understanding (e.g., the fact that a number of 'constants' in the sm are simply plugged-in from experimental data, and the underlying 'why' still not understood--the mass of the top quark for instance), and of course the fact that the sm does not, cannot, encompass gravity, until such time as the 'graviton' is found, is a celestial carrot over the physicist's head. 'why doesn't the standard model explain everything?' that's what keeps scientists up at night, not nobel prizes.

I think 'most' scientists would say they are not in the business of discovering "why", they are in the business of discovering "what" and "how". "Why" is best left to philosophers and theologians. The distinction may be small, but it's quite important to a lot of people.

That said, the politics of academia is as much a part of science as it is in lawmaking. The money has to come from somewhere, and that somewhere is controlled (in the US) by both the lawmakers AND fellow scientists who review each others grant proposals as well as the results. That's a very powerful reason for playing the political game for position. No grants means no work, no work means you don't get published, no published works means you don't get tenure assuming you can get a foot in the door to begin with!

to respond to those arguing that physicists may have ulterior motives for wanting new and theory-clasting breakthroughs, i.e.. fame, fortune, etc; i posit that while almost no human with an ego would deny the pleasures in having one's good works recognized, i would argue that the vast majority of physicists are in the game for the sheer love of understanding and discovery. and while the standard model is not broken or in need of trashing and starting over, there are a number of aspects that make it tantalizingly ripe for a re-think, or deeper understanding (e.g., the fact that a number of 'constants' in the sm are simply plugged-in from experimental data, and the underlying 'why' still not understood--the mass of the top quark for instance), and of course the fact that the sm does not, cannot, encompass gravity, until such time as the 'graviton' is found, is a celestial carrot over the physicist's head. 'why doesn't the standard model explain everything?' that's what keeps scientists up at night, not nobel prizes.

I think 'most' scientists would say they are not in the business of discovering "why", they are in the business of discovering "what" and "how". "Why" is best left to philosophers and theologians. The distinction may be small, but it's quite important to a lot of people.

That said, the politics of academia is as much a part of science as it is in lawmaking. The money has to come from somewhere, and that somewhere is controlled (in the US) by both the lawmakers AND fellow scientists who review each others grant proposals as well as the results. That's a very powerful reason for playing the political game for position. No grants means no work, no work means you don't get published, no published works means you don't get tenure assuming you can get a foot in the door to begin with!

to respond to those arguing that physicists may have ulterior motives for wanting new and theory-clasting breakthroughs, i.e.. fame, fortune, etc; i posit that while almost no human with an ego would deny the pleasures in having one's good works recognized, i would argue that the vast majority of physicists are in the game for the sheer love of understanding and discovery. and while the standard model is not broken or in need of trashing and starting over, there are a number of aspects that make it tantalizingly ripe for a re-think, or deeper understanding (e.g., the fact that a number of 'constants' in the sm are simply plugged-in from experimental data, and the underlying 'why' still not understood--the mass of the top quark for instance), and of course the fact that the sm does not, cannot, encompass gravity, until such time as the 'graviton' is found, is a celestial carrot over the physicist's head. 'why doesn't the standard model explain everything?' that's what keeps scientists up at night, not nobel prizes.

indeed, well, i didn't mean 'why' in the theological sense, more in the concrete explanation sense, relative to other knowns. and i wouldn't argue the rest of it. i have no doubt 'politics' plays a huge role in the nuts and bolts of securing funding for science, like in many fields. and publish or perish, etc, etc. yes. still, my point was.. well, was my point. and not in contrast to yours, just perhaps aside from.

Physicists too, I have a feeling, are sometimes hoping they will find something that breaks old models, to make a name for themselves and secure more funding perhaps.

While fame and fortune may play a role, I think there is a more fundamental aspect: there are certain things that he Standard Model just does not explain. Among them, why neutrinos have mass, why the universe has more matter than antimatter, what dark matter and dark energy are, and how gravity works.

Turtles. Turtles all the way down. I'll take all the nobel prizes forever now, thanks.

All those projects listed on page 1, and you forgot one of the longest running ones of all, the Muon1 distributed Particle Accelerator Design project, which (or rather was) part of the UK Government's Neutrino Factory project. As the name implies, it is working on Mu Neutrinos. I say was, because the project lead just moved from the RAL near oxford to BNL in Long Island.

But still, it's a slap in the face for those of us that've worked so hard on it, Ars readers included (Dave Peachy of the ArsTechnica team has been leading the stats on one of the sub-projects for most of the past year), and we've only done 84.3 MILLION SIMULATIONS running enough simulation data to simulate a particle almost to the edge of the Oort cloud, in 3mm steps.

Am I the only one that saw the cover pic and thought it was a remastered screen of V'ger from Star Trek 1?

And yes, my first thought was of V'ger in that first photo. But the rest of the photos were outstanding as well. Something about the mass and symmetry of high-energy physics detectors is just plain awesome for those of us not in the field.

All those projects listed on page 1, and you forgot one of the longest running ones of all, the Muon1 distributed Particle Accelerator Design project, which (or rather was) part of the UK Government's Neutrino Factory project. As the name implies, it is working on Mu Neutrinos. I say was, because the project lead just moved from the RAL near oxford to BNL in Long Island.

But still, it's a slap in the face for those of us that've worked so hard on it, Ars readers included (Dave Peachy of the ArsTechnica team has been leading the stats on one of the sub-projects for most of the past year), and we've only done 84.3 MILLION SIMULATIONS running enough simulation data to simulate a particle almost to the edge of the Oort cloud, in 3mm steps.

The only connection I can remember at the moment is to do with DogeCoin though this particular phrase may be something else. It is similar to the old to the old game that said "All your bases are belong to us."

Kepler thought the most important question in science was to understand why the Solar System had six planets.

Kepler was working at a time when physics and mysticism weren't clearly separated, and his model of the solar system was based on concentric Platonic solids, each of which determined the orbit of a planet. However, there are only five Platonic solids, and six planets (that he knew of). So the number of planets was off by one. Answering his question required a breaking away from his wrong belief about the role of Platonic solids in favour of a mechanistic view. This was ultimately accomplished by Newton, and amounted to a paradigm shift in science.

So the question was not silly at all. In general, the silliness of a question depends entire on the context.

Normal radioactive decay happens when an atomic nucleus sheds weight by converting a neutron into a proton, emitting a beta particle—an electron—and a neutrino.

Well, apart from all the other "normal" modes of decay that aren't beta decay, that is...

The article is actually right bout this. Natural radioactive decay is usually beta decay. Fission is quite rare, and alpha decay is not common, either. Pretty much every other naturally-occurring radioactive decay is some form of beta decay (e.g. electron capture, gamma emission, etc.).

Physicists too, I have a feeling, are sometimes hoping they will find something that breaks old models, to make a name for themselves and secure more funding perhaps.

While fame and fortune may play a role, I think there is a more fundamental aspect: there are certain things that he Standard Model just does not explain. Among them, why neutrinos have mass, why the universe has more matter than antimatter, what dark matter and dark energy are, and how gravity works.

In fact, the Standard Model has no suggestion as to why there is anything at all, though this may not be answerable if the explanation requires information from outside of observable spacetime.

Kepler thought the most important question in science was to understand why the Solar System had six planets.

Kepler was working at a time when physics and mysticism weren't clearly separated, and his model of the solar system was based on concentric Platonic solids, each of which determined the orbit of a planet. However, there are only five Platonic solids, and six planets (that he knew of). So the number of planets was off by one. Answering his question required a breaking away from his wrong belief about the role of Platonic solids in favour of a mechanistic view. This was ultimately accomplished by Newton, and amounted to a paradigm shift in science.

So the question was not silly at all. In general, the silliness of a question depends entire on the context.

Salute from another admirer of Kepler. Part of Kepler's problem was that the idea of nested Platonic solids worked so well and even appeared to "explain" the elliptical orbit of Mars (gap in the nesting). Bode's Law was treated for a long time as if it might have some underlying physical principle, but it seems to be just a coincidence. And of course we continue to refer to the bright stars by their constellations, which don't really exist.Astronomers are part of a very ancient and conservative scientific community, which is presumably why some of them are still so uptight about the "downgrading" of Pluto. Kepler, on the other hand, was a real shaker of the foundations and deserves his status.

Physicists too, I have a feeling, are sometimes hoping they will find something that breaks old models, to make a name for themselves and secure more funding perhaps.

While fame and fortune may play a role, I think there is a more fundamental aspect: there are certain things that he Standard Model just does not explain. Among them, why neutrinos have mass, why the universe has more matter than antimatter, what dark matter and dark energy are, and how gravity works.

Considering all (provable or counter-provable) possibilities is always the fundamental idea behind science, and I daresay physics the epitaph of it. Wave-particle duality was established only by "breaking" old models set by Newton, Maxwell and Hertz respectively in their time. Sometimes an oddity such as Technicolor pops up, but nonetheless challenging is an important part of the procedure.

As someone who often manages to write the wrong word while knowing the correct one, I think you mean physics is the epitome, not the epitaph, of scientific method.Physics is physics, mathematics is an abstract study which is sometimes useful in physics, and everything else is stamp collecting; it's just that sometimes the way the stamps are arranged is itself useful knowledge.

Physicists too, I have a feeling, are sometimes hoping they will find something that breaks old models, to make a name for themselves and secure more funding perhaps.

While fame and fortune may play a role, I think there is a more fundamental aspect: there are certain things that he Standard Model just does not explain. Among them, why neutrinos have mass, why the universe has more matter than antimatter, what dark matter and dark energy are, and how gravity works.

The other half of the reason it gets the attention(and why it gets to be called 'the standard model') is that it is stubbornly and frustratingly good at modelling the areas that it can handle; but years of theoretical and experimental work haven't managed to extend it to cover those outstanding vexing questions.

If it were just lousy, nobody would waste time poking holes in it. It's the "Oh, absolutely fantastic agreement between theory and experiment, right down to the noise floor, wonderful. Oh? Gravity? No idea whatsoever." thing that gets people.

"Even unmasking the mysteries of neutrinos may not thoroughly explain the matter-antimatter asymmetry, or how the nuclear forces unify, or how those forces relate to gravity, or what constitutes dark matter or, for that matter, dark energy."

While I think this is interesting research, I am somewhat upset over the attitude which may have been expressed in the opening. That is, something must upend or supersede existing models to be interesting or worthy. How interested is the public in learning the things that we already know, versus the things we are trying to find out?Physicists too, I have a feeling, are sometimes hoping they will find something that breaks old models, to make a name for themselves and secure more funding perhaps.

There are still important unanswered problems, and things to explore. I just think perhaps these attitudes are a bit unhealthy.

You can do good and useful science proving existing theories, sure. But face it, current physics is not so great. We have no antigravity, we have no FTL travel. I'm looking for big shake-ups too!

No antigravity, no FTL. I'd really like to hear about your plan for redesigning the universe, because if either of those things were possible on macroscopic scales, I think we'd have noticed by now.